In the reloading of containers, interchangeable superstructures, road truck units etc. these are raised and lowered vertically and are moved horizontally. In order to obtain high reloading rates, short movement periods are desired involving high accelerations and correspondingly high transverse forces.
Where load receiving means are suspended from ropes the travelling movements of the crane trolley and/or bridge result in swinging movements of the load receiving means, whereby a rapid gripping of the load is impeded. Where the load has already been picked up pendulum-like oscillations take place whereby an accurate setting down of the load, e.g. onto the chassis of a vehicle, is made quite difficult. The problem of pendulum movement also may result from wind action.
Although pendulum damping means are known in which the ends of the ropes are fixed to hydraulic cylinders, the operation of the hydraulic cylinders requires considerable control effort which can only reduce the problem of pendulum movements but can never eliminate it entirely.
Where the load receiving means are suspended from ropes which for trans-loading are to be firmly connected to the load the problem exists, in particular where the load is askew, that the load receiving means must be brought into the correspondingly askew position. Such positioning, in known apparatus involving traction ropes, is brought about by the aforesaid hydraulic cylinders. In spite of the control means required therefore considerable time delays may result where the load is in an askew position because of gravitational effects.
A particular problem results if the load--seen in a plan view--is angularly displaced in relation to the load receiving means. A pivoting of a load receiving means suspended from ropes is possible only to a lesser degree and with extraordinary effort.